Project Summary Osteoporosis affects more than 2 million men in the United States today and nearly 12 million more have osteopenia (34). Osteoporosis is the cause of 85% of all hip fractures and 90% of vertebral fractures in men (31), but, nevertheless, often goes undiagnosed and inadequately treated (56). Unlike women who are often identified as osteopenic or osteoporotic via routine DXA scan, men usually present with fragility fractures, back pain or diminishing stature (56). Even after suffering an osteoporosis-related fracture, >90% of men remain undiagnosed and untreated (6;36). Post-fracture, men are less likely to receive follow-up care than women (8), including calcium and vitamin D supplementation (37) and prescription of antiresorptive pharmacotherapy (22). The majority of osteoporosis treatment and prevention studies, including pharmacologic interventions, have been conducted in female populations. Although antiresorptive medications are an FDA-approved treatment for osteoporosis in males (18), less than 10% of men with osteoporotic fractures are treated with bisphosphonates. Enthusiasm for use of these medications in men appears to be limited by the relative lack of long-term safety and efficacy studies in men, the especially poor treatment compliance in males (47), and data suggesting poor cost effectiveness of bisphosphonate treatment in men (44). Exercise-based interventions are an attractive alternative to medication due to the reduced cost, fewer serious side effects, e.g., severe suppression of bone turnover (35) and gastrointestinal complications (18), and additional health benefits, including improved balance and fall reduction (45). Resistance training (21) and structured jump-training interventions increase BMD of the spine in girls and pre- and post-menopausal women (12;20;51) data supporting the efficacy of activity-based interventions to increase BMD in adult males with osteopenia are virtually non-existent. Because body composition (40) and hormonal status (28) modify bone response to mechanical loading, there may be gender differences in the response to exercise-based interventions. Moreover, the optimal exercise-based intervention with regard to mode, number of loading cycles, frequency of load cycles, etc. remains to be determined. Thus, studies that aim to identify safe and effective, yet practicable, exercise-based interventions to increase BMD in adult men with osteopenia are desperately needed. The overall goal of the proposed study is to compare the efficacy of a plyometric-based intervention to increase bone mineral content (BMC) and density (BMD) with that of resistance training and to explore the mechanism of changes in BMD by measurement of bone turnover markers and hormones in apparently healthy adult males with osteopenia of the spine and/or hip. We hypothesize that the efficacy of plyometrics will be greater than that of resistance training. PUBLIC HEALTH RELEVANCE: Project Narrative Although osteoporosis affects more than 2 million men in the United States today and nearly 12 million more have osteopenia, low bone mass often goes undiagnosed and inadequately treated in males (Wright 2006). The overall goal of the proposed study is to compare the efficacy of a plyometric-based intervention to increase bone mineral content (BMC) and density (BMD) with that of resistance training and to explore the mechanism of changes in BMD by measurement of bone turnover markers and hormones in apparently healthy adult males with osteopenia of the spine and/or hip.